hooking up big wire in a service panel

[mx842]

I want to run a circuit over to my big powder coat oven. I have a section of #4 copper in conduit that I want to use. I plan on putting a 100 amp service panel on the oven to use to power it and also to be used as a disconnect. There will be 2) 40 amp breakers 1 for each burner and a 20 amp circuit for a small fan and light.

My question is, do I have to run this circuit off of it's own circuit breaker in the main service panel or can I use the lugs under the main breaker in that panel to feed this sub panel. Space is getting low in my main panel and I didn't want to run 3 or 4 circuits out of that box to feed this equipment if I don't have to.

 

[jim111]

What size main service panel do you have? Is it meter-main or service panel? Home or shop? #4 copper not big enough for 100 amps unless carrying entire load of residence

 

[pattenp]

If those lugs are pass through lugs you can use them to feed the subpanel, but as said #4 Cu is not large enough for 100A, only 85A.

 

[mx842]

What is meant by pass through lugs??

 

[mx842]

I was just using the 100 amp panel because I already had it. The oven won't pull all 100 amps more like 60 when running full out. My main at my house is 400 amps. I split that in half and used 200 amps in both places. My shop is not attached to the main house so my neutral and ground lugs are not together.

 

[zmaxmotorsports]

Install a breaker in the main panel to feed it,order a smaller breaker to feed it with.

 

[ard]

I was just using the 100 amp panel because I already had it. The oven won't pull all 100 amps more like 60 when running full out. My main at my house is 400 amps. I split that in half and used 200 amps in both places. My shop is not attached to the main house so my neutral and ground lugs are not together.

You can't base the wire size on what "should" be.

If something goes wrong and your oven begins to pull more current- and doenst trip those breakers- say it is at 39+39+19=97A. The 100A breaker on the sub will not trip and you will be over-current on that main wire.

 

[jim111]

As stated by Zmax above, put a 70 amp breaker in your main panel feeding the new sub. #4 copper is good at 85 amp or less and if you only need 60 you should be good. Doesn't matter what size sub panel you use as long as you protect the wire feeding it with proper size breaker, and dont exceed the panel amperage rating

 

[pattenp]

What is meant by pass through lugs??

Non-fused lugs that are designed to add an additional feed to a secondary panel. Feeding a subpanel this way makes the main breaker in the sub the actual over current protection device (OCPD). Adding a breaker in the primary panel to feed the subpanel makes that added breaker the OCPD and the main breaker in the subpanel now acts as no more than a disconnect. So you could use a 80A or 90A breaker in the primary panel to feed the 100A subpanel and be okay using the #4Cu.

 

[mx842]

Well yesterday I went out and dragged that big azzed coil of wire into the shop to just see if it would be long enough to get from the panel to the oven. It was just long enough to make it but I will have to mount the panel a little higher than I originally planned. When I checked it closer I found that it's not #4 wire but it turned into #1 wire So wire size wont be a problem with the Amp load I'm working with. I don't know why I thought it was #4 but it was a long time ago when I got this wire coil for this project.

So back to my original thought..... 'pattenp' noted that if the lugs I was talking about were pass through lugs I could use them in the main panel. The lugs that are in my panel box are right below the main 200 amp breaker and are attached to the two hot buss bars that feed the breakers in the box. Hopefully this is what you were referring to as pass through lugs. I have a #1 neutral adapter kit for the neutral wire and the ground wire which is #4 I think should fit into the ground buss bar. Does this sound like a suitable plan?

 

[Radix2]

Well yesterday I went out and dragged that big azzed coil of wire into the shop to just see if it would be long enough to get from the panel to the oven. It was just long enough to make it but I will have to mount the panel a little higher than I originally planned. When I checked it closer I found that it's not #4 wire but it turned into #1 wire So wire size wont be a problem with the Amp load I'm working with. I don't know why I thought it was #4 but it was a long time ago when I got this wire coil for this project.

So back to my original thought..... 'pattenp' noted that if the lugs I was talking about were pass through lugs I could use them in the main panel. The lugs that are in my panel box are right below the main 200 amp breaker and are attached to the two hot buss bars that feed the breakers in the box. Hopefully this is what you were referring to as pass through lugs. I have a #1 neutral adapter kit for the neutral wire and the ground wire which is #4 I think should fit into the ground buss bar. Does this sound like a suitable plan?

I think something is missing here- if you are going to use the pass through lugs ( the main is your only protection for the wire to your sub) then you need to size the feed to the sub to carry the full rating of the main. In your case your protection is a 200A breaker, so your sub feed needs to be sized for 200A, so you cannot use #1 or #4 wire.

The best plan would be to put in a new 100A breaker in your panel to feed the sub with your #1 wire.

 

[pattenp]

Those lugs sound like they are protected by the main 200A breaker. If they are actual lugs that are open/empty then they can be used to feed the subpanel. Make sure you are not confusing the connection screws that fasten the buss bar to the main breaker. A picture would be great.

 

[pattenp]

I think something is missing here- if you are going to use the pass through lugs ( the main is your only protection for the wire to your sub) then you need to size the feed to the sub to carry the full rating of the main. In your case your protection is a 200A breaker, so your sub feed needs to be sized for 200A, so you cannot use #1 or #4 wire.

The best plan would be to put in a new 100A breaker in your panel to feed the sub with your #1 wire.

Very good point, I didn't think about that to mention it.

 

[mx842]

Thanks guys.............I guess I'll have to step back and punt so to speak. Thanks for helping me sort this out.

 

[Zeke]

I was just using the 100 amp panel because I already had it. The oven won't pull all 100 amps more like 60 when running full out. My main at my house is 400 amps. I split that in half and used 200 amps in both places. My shop is not attached to the main house so my neutral and ground lugs are not together.

Can you clarify that a bit?

You have a 400 amp main and it's almost full?

You split 200 off to where?

 

[mx842]

Can you clarify that a bit?

You have a 400 amp main and it's almost full?

You split 200 off to where?

When I built my house I put in 400 amp service. The power company didn't want to do it because at the time most residential hook ups were 150 amps. I argued with them and with the help of a few extra bucks I finally got what I wanted. I knew I was going to build a shop out back someday and that shop would have welders, milling machine, lathe, and yes a small powder coating setup.

When the electricians installed the service they used 2) 200 Amp service panels with most of the circuits in one of the boxes and a few in the second box. I moved those circuits out of the second box and put them in the first panel and used the second box to feed my shop. Hopefully that made sense.

I put a 200 amp panel in the shop and yes that panel is almost full I have room for just a couple more circuits in there. I'm thinking that some day I'll have a dedicated service put in just for the shop, that is if I ever get it set up and running the way I want and things pan out like I hope they will.

 

[Zeke]

Where I got confused is when you said, "Space is getting low in my main panel..." when you meant your subpanel in the garage.

I don't see any difference in installing a breaker to feed the new subpanel on the oven or doing the feed through, if the panel is so equipped, and installing a main breaker in the oven panel. What am I missing? Obviously, you do need more breaker space so the 2nd subpanel makes sense. You will need to run 4 wires to the 2nd subpanel and connect to a new ground rod or 2.

Whether you use over current protection upstream or downstream, or both, is of little consequence. That's the way I read it, I may be wrong.

 

[pattenp]

You will need to run 4 wires to the 2nd subpanel and connect to a new ground rod or 2.

Why would there be a need for another set of ground rods at the shop for the second subpanel? There should already be ground rods connected to the first subpanel in the shop.

 

[zmaxmotorsports]

Why would there be a need for another set of ground rods at the shop for the second subpanel? There should already be ground rods connected to the first subpanel in the shop.

 

[Zeke]

Why would there be a need for another set of ground rods at the shop for the second subpanel? There should already be ground rods connected to the first subpanel in the shop.

I'm sure you're correct, but it seems as if the code wants a ground rod for every panel. If in the same building, I guess that's the exception.

 

[Radix2]

I don't see any difference in installing a breaker to feed the new subpanel on the oven or doing the feed through, if the panel is so equipped, and installing a main breaker in the oven panel. What am I missing? Obviously, you do need more breaker space so the 2nd subpanel makes sense. You will need to run 4 wires to the 2nd subpanel and connect to a new ground rod or 2.

Whether you use over current protection upstream or downstream, or both, is of little consequence. That's the way I read it, I may be wrong.

Yes, you are wrong.

One obvious fault to be protected against is the wire from point A to point B becoming shorted...protection downstream from that fault...is no protection at all.

Hence the requirement that wire downstream from a Ocpd needs to be sized to properly trip the upstream OCPD.

If he uses the lugs, he is only protected by the 200a main breaker - so his wire needs to be sized for that. If he puts in a smaller breaker to feed the subpanel, then he can use smaller wire.

Being required to run 200a wire to a 100a subpanel is a costly waste IMO.

 

[prostreetamx]

Your 200a sub panel in your shop should have 40 breaker spaces. This can be done with all full size breakers, twin breakers or a combination of both depending on the buss bars. Someone may have filled up all the spaces that were designed for twin breakers with full size breakers, causing your fill issue. If you don't have 40 spaces available either look at the decal or pull out a few breakers to see if any of the buss bars have slots in them that allow you to fully seat a twin or quad breaker. If that is the case, buy some twins and move some stuff around to give you 2 full size spaces for your 100a sub panel breaker. If you can provide a pic or a panel model number, there are a few guys on here that can tell you if that is the case.

 

[mx842]

Your 200a sub panel in your shop should have 40 breaker spaces. This can be done with all full size breakers, twin breakers or a combination of both depending on the buss bars. Someone may have filled up all the spaces that were designed for twin breakers with full size breakers, causing your fill issue. If you don't have 40 spaces available either look at the decal or pull out a few breakers to see if any of the buss bars have slots in them that allow you to fully seat a twin or quad breaker. If that is the case, buy some twins and move some stuff around to give you 2 full size spaces for your 100a sub panel breaker. If you can provide a pic or a panel model number, there are a few guys on here that can tell you if that is the case.

I do have a couple spaces left in that main panel but I wanted to hold on to them for future circuits I have plans for in that part of the building. I guess at this point I'll just add this circuit and later on I can go the twin breaker route if needed.

I have two spare runs of conduit running into this panel to places where I can get to so I can add circuits. Flush mounted panels look better but are a pain to get to, to run new circuits if needed.

 

[Zeke]

Yes, you are wrong.

One obvious fault to be protected against is the wire from point A to point B becoming shorted...protection downstream from that fault...is no protection at all.

Hence the requirement that wire downstream from a Ocpd needs to be sized to properly trip the upstream OCPD.

If he uses the lugs, he is only protected by the 200a main breaker - so his wire needs to be sized for that. If he puts in a smaller breaker to feed the subpanel, then he can use smaller wire.

Being required to run 200a wire to a 100a subpanel is a costly waste IMO.

Copy that.

 

[prostreetamx]

If you have 4 full sizes spaces left you have 2 for your 100a load and 2 more so you can simply add another small sub panel later. Personally I don't like to go with the thinner breakers on any load over 30a, especially if it is a continuous load since those smaller frame breakers get hot fast. They do make quad breakers with up to 50a in the center pair but I don't like to use them if there are other options. I live in Las Vegas and most of our main panels here are located outside in the hot sun. Probably not a major issue for indoor panels of cooler climates. My new 150a garage panel is located indoors. It is only fed with 100a but I used it to give me more breaker spaces than a common 100a panel has to offer. I also like the fact that since it has a main breaker inside I can kill it to work on it without going outside to my main panel.